Re: Great short distancer runners but Mother Nature left out the brains! - Page 6

 

Vito wrote:


I just see that I asked unnecessarily in my other post for clarification.
Feel free to ignore it.
 

Do you understand what conservation of angular momentum means?  It means
that without an external force applied, you cant change the value of
angular momentum of the system.  In our case it means that if you lean one
way on the bike, something mus lean the other way, just to preserve the
angular momentum of the system.

IOW, if you are able to lean into the bend without "something" leaning out
of the bend, you violate the law of nature.


Outside?  Then yes.  This way you can make the bike lean into the corner.  


Maybe.  Now just wrap it all in an appropriate mathematical model and post
it to Am.J.Phys as a critique of J. Fajans's work.  They published one
article criticizing an accepted model of bike handling already, so no
reason to assume that they won't do it again.


Currently accepted model of bike handling requires that the wheel be
pointed "the wrong way" to initiate the turn, though, so you are going
against what is currently published.  I'm not saying that currently
accepted model is necessarily right.  I just don't feel compelled to
believe you, especially until you have some math to support your view on
things.


So called camber thrust?  It matters relatively little, IMHO.  A bike with
squared tires or square tires will still self steer in corners, though in a
less predictable way.  I used to ride Urals solo with sidecar tires on, so
I know from experience how it works.  Well, it does, somehow.


Here we agree.  
 

You are actually onto something here.  Just not what I would consider truly
important.  We can't tell who is right until we do the math and compare
results.  The math describing bike behavior in terms of countersteering or
gyroscopic precession is already done.  Camber thrust was mostly ignored up
to now, as far as I can tell, so you are more than welcomed to prove
everybody wrong by showing how important it really is.  (I just read my
post, checking for errors, and it came to me that once I tried to solve
this problem.  It was so long ago, that it came to me just now.  I didn't
try very hard, just enough to admit that I can't solve it easily, but it
would be actually interesting to see how one should approach it.)
 

Here we agree, too.  I really read what you write and try to understand what
you have to say.  I mean it.  And you seem to be mostly right, IMO.
 

Turning the bars loads the front, so you don't take the weight off it.  


Yeah, that would be roughly what I think too.
 

I seriously think that you are missing the point here.  Nobody in his right
mind ever said that body-steering is universally impossible.  For example
it works fine on a bicycle, and everybody can try it for themselves
whenever they feel the need.  In general it will work much better on a
light machine than on a heavy one, it will work better at slow speeds than
at high speeds, and it will work better on bikes with sharp steering than
on bikes which steer slowly.  But it will work to a point on every two
wheeler.  

Now, the point is what really works?  Not what somehow works, almost works,
works on a specific bike, on smooth and level road etc.  I firmly believe
that using conscious countersteering is how you should ride any bike.  You
guys claiming to be able to achieve some level of control without using it
convince me not.  Some level of control is not what I call control.

--
Andrzej Rosa

 


The CG height relative to the displaced contact patch is lower when the bike
is leaned. The bike and rider can approach free fall during the
countersteer, unweighting the contact patch.

(Every spring for quite some time, the first time I got on a bicycle that
season, I would countersteer the bicycle with the same force I would
countersteer a motorcycle, which has the effect of immediately laying the
bicycle on its side. The combined system -- me and the bicycle -- were in
free fall for that brief instant. Human reflexes are astonishingly fast when
unemcumbered. The first two times, a year apart, I managed to put the foot
down in time to keep from falling, and then haul up on the handlebars with
the same force I would use to save a motorcycle from over tipping, with the
foreseeable consequence. The third year, I stumbled on the uneven pavement,
and was not able the prevent the fall. The sprained ankle hurt much less
than "saving" the bike. I gave up on bicycles after that, for other
reasons.)

 

MikeWhy wrote:


When you go through a chicane, your forks get compressed (easy to see).
Once you are in the turn, centrifugal force will take care of compressing
them, and just to keep things in perfect balance you should actually be
slightly accelerating through the turn, thus deloading the front a bit.
Rear tire is wider and has a bigger contact patch, even when you lean hard,
so this is a better way of making use of the grip which is available to
you.  

Now, how to actually explain that when you turn the bars you load your
front?  I'm really struggling a bit here, so let me think.

Let's put it this way.  When you ride forward, your front wheel can turn
freely, when you turn the bars, it starts going sideways, due to friction
of the tire.  This friction wasn't there before you turned the bars, hence
it is a new force, which opposes your bike's forward motion.  You got the
force in front, so you load the front.   I hope this helps.


Scary, isn't it?  I tried this very thing today on purpose.  You can lean a
pushbike damn fast.


I never had this problem.

--
Andrzej Rosa

 



Don't hurt your head that way, but thanks for the help. ;)

CG height above ground when leaned over is some distance lower than when
you're upright. At some point between cornering left and cornering right, in
your chicane example, the bike will pass through upright. It's CG height is
highest at this point. Need I continue? As the bike continues to lean now in
the other direction, the CG height again falls. Normal load on the contact
patch also falls. Thus, the contact patch unloads somewhat through the turn
setup.

All through this, "centrifugal" force while upright is negligible, but don't
tell your suspension that. It hasn't had time to fully respond to the change
in load. The dampers and unsprung mass resist the spring's extension,
contributing to the loss of load at the contact patch.

Last, steering action is far from instantaneous, and the front tire doesn't
"go sideways" in the sense that you mean. Flipping from full left to full
right, the slip angle and coning angle change, but are still in the tire's
normal operating range. Peak lateral stiffness is in this range. Pushing the
slip angle beyond peak causes the front to slide and washout, resulting in a
low side, rather than generating more lateral force. The condition is
especially dire for the road racer (compared to street riding, referencing
your use of "chicane"). In a steady state turn, he is presumably at
cornering limit on the front tire, or would like to be. However, this leaves
no cornering potential with which to countersteer.

Anyway... the front is unfavorablly loaded while transitioning into and out
of a turn, for all the reasons given. You or I wouldn't normally notice
them, since we had already shit our drawers well before even getting close
to traction limit. I kinda like it that way.

 

MikeWhy wrote:


Why, I wore a helmet, of course. ;-)
 

No, you a right here, and that's why front is loaded when going through a
chicane.  I just used it as an "easy to see" example.


You don't countersteer by this time anymore.  Countersteering is needed to
initiate the turn (which loads the front some), but later on you don't
countersteer.  
 

You mean that leaning your bike fast is scary?  Sure it is.  That's why you
need balls to be a good racer (which I'm lacking).
 

Yeap.  Good racers are able to turn so fast that their front creeps.  It's a
mighty impressive thing to even contemplate. (Though I had mine wash out
from under me in the wet once, I was able to save it.  Funny how it works,
but when your front sleeps under you when you try to initiate the turn, you
simply do not turn, or at least not much, so I was able to save it.)


They try to avoid any corrections midturn.  They are trained to avoid them.
It takes balls, talent and some magic to be a good racer.
 

Nope.  While you initiate the turn, your front gets loaded.  If you want to
straighten your bike, your front gets loaded too.  Midturn you rely on
centrifugal force.


That was my point.  It takes a really fast cornering to come even close to
the limit (barring oil, sand and other such niceties).


Like it or not, I'm not ballsy enough for doing it on the limit.

--
Andrzej Rosa